Evaluation of Vertical Coherence Length, Twist and Microstrain of GaAs / Si Epilayers Using Modified Williamson-Hall Analysis

Modified Williamson-Hall (WH) analysis is used to determine the reliable values of the microstructures for Zincblende epilayers grown on non-polar substrates. Systematic high resolution X-ray diffraction (HRXRD) experiments are performed for several skew symmetric reflections which enable an accurate measurement of the values of vertical coherence length (VCL) and microstrain of GaAs epilayers grown on Si. Furthermore, a simple method based on the orientation of Burgers vector is proposed for estimating the ratio of tilt and twist. In this method, the twist can be found easily once tilt is known. It is rather quick and the measured values of twist are very similar to those which are otherwise estimated by acquiring numerous HRXRD scans along with tedious fitting procedures. Presence of 60 mixed dislocations is confirmed from the cross sectional high resolution transmission electron microscope images of GaAs / Si samples. Furthermore, the estimated value of VCL is equivalent to the layer thickness measured by the surface profiler.